This invention relates to a toner conveyance device and an image forming apparatus of an electrophotographic method having the toner conveyance device.
In a high-speed image forming apparatus or a color image forming apparatus, because the capacity of the toner storage unit for storing the toner is large, there is a problem that it sometimes happens a case where it is difficult to dispose the toner storage unit in the neighborhood of the development device.
As regards means for solving such a problem, it has been developed a toner supply technology in which toner particles are conveyed from the toner storage unit to the development device by a toner conveyance method called an air conveyance method which is capable of conveying toner particles to a distant place.
The basic structure of a toner supply device using an air conveyance method is composed of a toner mixing portion for mixing toner particles with air, a conveyance means for conveying a toner fluid produced by the mixing of toner particles with air in the toner mixing portion, and a toner separation portion for separating toner particles from the conveyed toner fluid.
However, in a conventional toner conveyance technology, when a mix fluid of toner particles and air is conveyed from the toner storage unit to the development device by a fluid conveyance means such as a pump, air is introduced into the toner mixing portion from the outside, and after the fluid is further separated into toner particles and air in the toner separation portion, the air is discharged through a filter to the outside. Accordingly, because an extra energy for introducing air into the device and further discharging the air to the outside of the device is required for the pump, it has been difficult to make the toner conveyance distance long. Besides, for the reason that the filter comes to clog up with toner particles or the like, there has been a problem that a stable toner conveyance cannot be practiced.
Further, most of the device has a structure such that the fluid flows back to the aforesaid fluid conveyance means without discharging a part of the air separated from the toner particles to the outside. Further, in the toner separation portion, there is provided a filter for not scattering toner particles to the outside, by which only a part of the air is made to flow to the outside to carry out the air pressure adjustment in the conveyance path (for example, the Japanese publications of the unexamined patent applications H7-219329, H10-97130, H10-268641, and H10-299672).
In a conventional technology, because a mix fluid of toner particles and air is conveyed to a toner separation portion disposed at a sufficiently distant position from a toner storage unit by a fluid conveyance means made up of a pump for conveying the mix fluid, the toner conveyance performance is not sufficient, and a poor conveyance sometimes occurs. For that reason, it is necessary to make the pump large-sized; however, if the pump is made large-sized, the amount of exhaust to the outside through the filter provided in the toner separation portion becomes large, which increases the toner quantity adhering to the filter to cause the filter to clog up earlier, and it results in toner scattering and requires a troublesome operation such as the replacement of the filter at the time of a periodical maintenance.